Apparatus for separating dry granular material

ABSTRACT

Separator apparatus embodying an inclined porous deck having parallel transverse upper grooves at right angles to its direction of inclination. Granular material deposited onto the upper end of the inclined deck is assisted by low pressure air forced upwardly through the deck in moving toward the lower end of the deck, the air effecting separation between granules or particles of greater specific gravity and granules or particles of lighter specific gravity, the former dropping to the bottom of the grooves while the latter float upwardly and flow progressively from groove to groove toward the lower end of the porous deck. The downstream sides of the grooves make an acute angle with the upper face of the inclined porous deck to entrain greater specific gravity particles in the grooves.

United States Patent 1 Johnston et al.

[ 1 Dec. 11, 1973 APPARATUS FOR SEPARATING DRY GRANULAR MATERIAL [75] Inventors: Norris Johnston; Mark Latker, both of Ojai, Calif.

[73] Assignees: Albert M. Clark; John C. Manning,

Bakersfield; John G. Troster, Atherton, Calif. part interest to each [22] Filed: May 27, 1971 [21] Appl. No.: 147,545

Related US. Application Data [63] Continuation-impart of Ser. No. 863,989, Oct. 6,

1969, Pat. No. 3,667,601.

Primary Examiner-Frank W. Lutter Assistant Examiner-Ralph J. Hill Att0rneyBernard Kriegel and Kendrick, Subkow &

Kriegel [5 7] ABSTRACT Separator apparatus embodying an inclined porous deck having parallel transverse upper grooves at right angles to its direction of inclination. Granular material deposited onto the upper end of the inclined deck is assisted by low pressure air forced upwardly through the deck in moving toward the lower end of the deck, the air effecting separation between granules or particles of greater specific gravity and granules or particles of lighter specific gravity, the former dropping to the bottom of the grooves while the latter float upwardly and flow progressively from groove to groove toward the lower end of the porous deck. The downstream sides of the grooves make an acute angle with the upper face of the inclined porous deck to entrain greater specific gravity particles in the grooves.

4 Claims, 6 Drawing Figures Law piss-raze- 17/2 J'UPPL s APPARATUS FOR SEPARATING DRY GRANULAR MATERIAL This application is a continuation-in-part of United States application Ser. No. 863,989, filed Oct. 6, 1969, for Apparatus for the Dry Separation of Granular Materials" now Patent No. 3,667,601.

The present invention relates to separator apparatus, and more particularly to apparatus for separating granular material in a dry state.

In applicants above-identified application, an apparatus is disclosed in which a blanket of dry material moves along a porous grooved bed while the bed is being vibrated and air forced upwardly through it to fluidize the material, the denser particles settling out and becoming trapped in the grooves while the gangue or worthless fractions of the material proceed along the bed for removal at its downstream portion. The prior apparatus is very effective in separating the material, but the necessity for vibrating the porous bed requires the various parts to be rigid and, therefore, of comparatively heavy, strong and sturdy construction. Vibrators, spring supports, vibration absorption devices, levelling devices, and other equipment, are necessarily included, which adds considerably to the complexity and cost of the equipment, as well as to the cost of maintaining it in proper working order and adjustment for optimum performance. The vibration of the bed limits the bed length that can be used, correspondingly limiting the capacity of the apparatus.

It has been found that a large percentage of the gangue or worthless sand, or other material, can be removed initially with a high recovery of the heavier values without vibrating the porous deck. With a nonvibration deck, the apparatus is much simpler since all vibrating equipment is omitted. Moreover, the framework can be lighter and, therefore, less costly. Maintenance costs are also reduced. The absence of vibration enables the porous bed or deck to be made much longer, resulting in much higher recovery of the valuable denser particles as the fluidized blanket flows along the bed.

Despite the high recovery of denser materials with the non-vibrating porous deck, it is usually desirable to employ the vibrating type of apparatus, described in the above-identified patent application, for final high purification of a mineral concentrate.

In addition to the foregoing objectives, that include simplicity, economy and greater capacity of the apparatus, a grooved porous deck is provided in which the deck has greater retentivity of the heavier particles in its grooves, particularly with the deck disposed in a downwardly inclined position with respect to the direction of travel of the material along the deck.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense.

Referring to the drawings:

FIG. 1 is a side elevational view, with portions in section, of an apparatus embodying the invention;

FIG. 2 is a top plan view of the apparatus shown in FIG. 1;

FIG. 3 is an end elevation of the apparatus taken along the line 3-3 on FIG. 1;

FIG. 4 is a cross-section taken along the line 4-4 on FIG. 1, illustrating the deck of the apparatus tilted to a dumping position;

FIG. 5 is an enlarged cross-section through the deck of the apparatus; and

FIG. 6 is an enlarged fragmentary section through the porous bed of the apparatus.

The apparatus disclosed in the drawings includes a frame structure 10 having a base 11, longitudinally spaced vertical standards or supports l2, 13 secured to and extending upwardly therefrom. The upper portion of the rear standard or support 13 is vertically adjustable, while the forward standard 12 may be of a fixed height. This latter standard is secured to a forward bearing support 14 by a pivot pin 15, a rear bearing support 16 being secured by means of a pivot 17 to the upper end of a toggle type of jack 18, of known construction, such as used in raising and lowering portions of vehicular trucks, the lower portion of such jack being secured to the fixed rear standard 13. Rotatably mounted in the bearings l4, 16 is a heavy pipe 19 that extends longitudinally beyond each bearing. The rearward end of the pipe 19 is connected through a suitable valve 20 to tubing 21 through which low pressure air can be fed, the forward end of the pipe also being secured to a valve 22 connected to a tubing or conduit 23 through which low pressure air can be supplied to the pipe. The pipe has an intermediate traverse wall or closure 24 therein, separating it into forward and rearward sections 19a, 1%, the lower portions of each section being provided with perforations 25 through which air is fed into an air chamber or plenum 26 through which the pipe extends, the plenum also being separated by an intermediate wall 27 into forward and rearward chamber portions 28a, 28b. The plenum is suitably affixed to the pipe 19 for movement therewith as a result of arcuate movement of the pipe 19 in its supporting bearings 14, 16.

The plenum includes a bottom wall 29 and a first side wall 30 extending upwardly therefrom. A second removable side wall 31 extends upwardly from the bottom of the plenum, with its upper end portion 32 tapering or flaring outwardly. Parallel mounting strips 33 are suitably secured to the inner faces of the side walls 30, 31 intermediate their vertical heights and on which a permeable deck 34 is supported, these strips being preferably narrow so as to avoid substantial impairment of the vertical flow of air from the plenum upwardly through the permeable deck or bed. The bed 34 is clamped between the side walls 30, 31 by means of Iongitudinally spaced tie rods 35 that extend transversely across the plenum, the tie rods extending through the strips 33, with one end of each tie rod being suitably secured to one of the side walls 30 and the other end portion extending through the removable side wall 31, a wing nut 36 being threaded on the outer portion of each tie rod and engaging a suitable clamp member 37 that bears against the outer face of the movable side wall 31. Tightening of the wing nuts 36 will retain the lower end of the movable side wall 31 against a recessed shoulder 38 in the bottom wall 29 and cause the upper portion of the movable side wall to engage one side of the deck 34, holding the other side of the deck against the other side wall 30. Thus, plurality permeable bed 34 rests upon the supporting strips 33 and is clamped between the side walls.

The deck or bed preferably comprises a pluraltiy of individual plates 34 that abut each other, being clamped between and against the side walls 30, 31. The sides of these plates preferably have thin sponge rubber strips 39 clamped between the deck sides and the side walls 30, 31 to prevent air leakage from the plenum 26 upwardly between the side walls and the deck. Partial loosening of the wing nuts 36 allows replacement and exchange of one or more plates 34a, which may have become damaged during operation of the apparatus, thereby obviating the necessity for replacing the entire deck, as in previous devices.

The permeable deck 34, which, for example, may be made of a material marketed by Ferro Corporation of Cleveland, Ohio, under the trademark Filtros, has a plurality of transverse grooves 40 in its upper face disposed perpendicular to the direction in which the granular material flows longitudinally along the bed, as described hereinbelow. The grooves are parallel to each other,'their width and depth and separation from one another being determined to provide the most effective recovery of the valuable heavier particles from the material flowing downwardly along the deck. A typical groove arrangement is one in which the width of each groove is about one-quarter of an inch, the depth of the groove also being a quarter of an inch, with the lands 41 between adjacent grooves having a width of about one-quarter of an inch. The side walls 42, 42a of each groove are inclined to the upper face 43 of the deck, the downstream side 42 of each groove making an acute angle R with the upper deck face in order to provide greater retentivity of the heavier particles of material in the grooves that settle thereinto while low pressure air is travelling upwardly through the porous deck, the air fluidizing the dry granular material flowing downwardly along the inclined deck, the upper or rear end 44 of which is at a substantially higher elevation than the forward or lower end 45.

The dry granular material to be separated is dropped down onto the rear end 44 of the inclined deck 34. This material is conducted from a suitable source into a hopper or feed bin 46 suitably supported by the framework above the deck 44 and plenum 19. The material drops from the feed bin and through a bin chute 47 onto the upper rear end 44 of the deck, the flow of material from the feed bin into the chute and onto the rear end of the deck being controlled by a gate 48 extending across the feed bin or hopper, this gate being inclined in a downward and forward direction and being slidable through a slot 49 in the hopper. The opening or gap 50 between the forward end of the gate and the opposed forward wall of the hopper or bin is controlled by a handle 51 rotatably mounted in a bracket 52 suitably secured to the rear portion of the hopper 46 and threaded within a nut 53 attached to a flange 54 suitably secured to the gate 48. Rotation of the handle 51 in one direction or the other will effect corresponding sliding of the gate 48 within the hopper to determine the size of the opening or gap 50 between the end of the gate and the hopper wall, and, thereby, the rate of downward feed or dropping of the granular material through the bin chute 47 and onto the rear portion 44 of the permeable deck.

At intervals, the flow of material from the feed bin or hopper 46 onto the deck is to be stopped or prevented. This action is effected by a check gate 55 in the hopper disposed below the flow gate 48. This check gate has a hinged connection 56 with the hopper and normally extends downwardly along the forward wall 460 of the hopper to permit the material topass from the hopper downwardly onto the porous deck. When the discharge end of the hopper is to be closed by the check gate 55, air is fed into the head end of the cylinder 57 that has a pivotal connection with a bracket 58 secured to the hopper 46, the air driving a piston 59a and piston rod 59 downwardly of the cylinder, which has a pivotal connection 60 with an arm 61 affixed to the check gate 55 and extending outwardly of the hopper. Normally, in the absence of air under pressure fed into the head end of the cylinder, the weight of the check gate 55 swings it downwardly into an ineffective position to force the piston rod 59 and piston 59a upwardly in the cylinder. However, when air from a suitable air supply under the control of a solenoid operated valve 62 is allowed to pass into the cylinder through a suitable tube or hose 63, the gate 55 is swung upwardly in the hopper to a position closing its discharge end. The valve 62 controlling the air supply is operated by a solenoid 64 electrically connected to a suitable timer switch (not shown). When the solenoid is energized, it shifts the valve 62 to permit air to flow to the cylinder 57, and, when deenergized, it will position the valve to shut off the air supply and open the line 63, leading to the cylinder, to atmosphere, permitting exhaust of air from the cylinder and the dropping downwardly of the valve 55 to open position.

As described more particularly hereinbelow, low pressure air passes through the pipe 19 and its perforations 25 into the air chamber sections 28a, 28b, then flowing upwardly around the pipe and through the porous bed 34, causing fluidizing of the material dumped upon the upper end of the bed and its downward progression over the grooved bed, the heavier valuable particles settling into the grooves 40 and being retained therein. A suitable supply of granular material is deposited on the upper end 44 of the permeable bed 34, as permitted by the valve mechanism 55. The apparatus operatesto effect separation of the granular material as it flows downwardly along the inclined bed for a predetermined period, whereupon valve 55 is closed and the material on the bed is dumped into a suitable trough structure (not shown), or the like, disposed at one side of the pivoted structure, the trough arrangement, by way of example, being as disclosed in the aboveidentified patent application.

Pivoting of the apparatus to dump the material on the bed is effected by air under pressure entering the rod end of a cylinder suitably secured at its lower end to the frame 10 of the apparatus, such air acting upon a piston and rod mechanism 71 to move the latter downwardly in the cylinder, the upper end of the rod being connected to a cable 72 wound around a grooved pulley 73 fixed to the pipe 19 at the rear end of the apparatus. Downward pulling of the cable 72 by the piston and rod device 71 causes partial rotation of the pulley, which, for example, may be through an arc of about to shift the entire plenum from a horizontal position, dumping the material on the permeable bed 34 onto the trough (not shown, but referred to above), the flaring side portion 32 of the plenum unit 26 facilitating such dumping. As the plenum unit and pipe are rotated by the pulley 73, a return spring 74 is tensioned, such return spring, for example, being disposed at the base 11 of the frame, one end being secured to such base and the other end being secured to a cable 75 that passes around a guide 76 and upwardly around a second grooved pulley 77 suitably affixed to the pipe. The bleeding of compresed air from the tilting cylinder 70, after the dumping operation has been completed, will permit the tension spring 74 to act through its cable 75 and pulley 77 to pivot the plenum back to its initial horizontal position, as determined by engagement of a suitable stop 78 mounted on a plenum counterblaance mechanism 79 with the upper end of a companion stationary stop member 80 affixed to a vertical rod 81 having a lower threaded end extending through a bracket 82 suitably secured to the rear standard 13, the stop rod 81 being adjustable as a result of upper and lower nuts 83, threaded on'the threaded rod portion, engaging upper and lower sides of the bracket 82. It is evident that the position of the upper end 80 of the stop can be determined by suitable threaded positioning of the nuts 83 on the threaded portion of the rod 81.

The high pressure air supply to the tilting cylinder 70 passes through a suitable valve 84 and through a tube 85 leading to the rod end of the cylinder. The opening and closing of this valve and bleeding of air from the cylinder is determined by a solenoid 86 that controls operation of the valve, this solenoid also extending to a suitable electrically operated timer (not shown) which controls the passage of current to the solenoid.

The counterbalance mechanism 79 is provided to facilitate pivotal movement of the entire deck assembly 26, 34 during its movement between its horizontal position and its dumping position. As shown, the counterbalance mechanism includes longitudinally spaced end members 90 affixed to the bottom of the plenum 26, a counterbalance bar 91 extending between and being suitably secured to the transverse or end members.

In the operation of the apparatus, the slope of the deck 34 is predetermined and is set through appropriate adjustment of the toggle jack 18 at the rear end of the apparatus. At the commencement of a cycle of operation of the apparatus, the deck assembly is in its fully upright position, the flow control valve 55 being in its open position and the material flowing from the feed bin 46 and through the bin chute 47 onto the upper end 44 of the permeable deck. Air under a suitable pressure passes through both low pressure air supply pipes 21, 23 and through the open valves 20, 22 into the mounting pipe 19, the air flowing into the plenum 26 and then moving upwardly through the permeable bed 34, the air flow through the bed fluidizing the dry material and causing it to flow from the rear por tion of the bed toward its forward portion 45, the particles of greater specific gravity settling out into the grooves 40 and becoming trapped therein, the gangue material at the forward end of the bed passing therefrom onto a suitable conveyor belt (not shown) for transport to a point of discharge. Air at slightly different pressures may be applied to the upper (rear) and lower (forward) portions of the deck, since the upper part of the deck becomes filled with heavy grains of material before the lower half and may require slightly more air flow to keep the ore fluidized for progressive downward movement along the bed. Each valve 20, 21 may be suitably adjusted to provide the desired air pressure and air flow for any given ore that is being concentrated, and to provide different degrees of pressure, if required, passing into the rear and forward portions of the plenum.

As pointed out above, the lower face 42 of each deck groove 40 is not vertical, but slopes downwardly with respect to the upper face 41 of the deck or bed in the direction of ore travel. This enables the smaller and lighter mineral grains, which are not totally freed from the gangue, to remain in the grooves 40 since they cannot climb the downstream side 42 of each groove and move into the next groove. These lighter grains are close to the density of the valuable minerals to be recovered, and they should likewise be recoverd, if at all possible. It is found that substantial additional recoveries of valuable minerals is achieved through slanting the forward or downstream faces 42 of the grooves in the manner described. By way of example, by inclining the permeable bed 34 15 to the horizontal, and with the inclined lower groove faces 42, it is found that the valuable lighter minerals are incapable of scaling the downstream faces 42 of the grooves and will be trapped therein. Grooves 40 making an angle of to the upper face, which is 20 from the perpendicular to the upper face 41 of the bed, effect satisfactory performance of the apparatus, although such angle can be varied from the specific figure given, ranging from about 10 to about 45 from the perpendicular to the upper face of the porous deck. The net effect of the slanting grooves 40 is to retain the heavy values of material better, increasing recovery and purity of the concentrate.

The deck assembly is dumped periodically, under the control of a timer (not shown). Prior to tilting of the deck assembly, the ore feed is shut off a few seconds by 1 the timer, causing the solenoid 64 to actuate the valve 62 and effect closing of the ore flow control valve 55. This short period allows the ore blanket to run off the forward end 45 of the deck 34 for disposal. With the flow control valve 55 closed, the timer effects opening of the high pressure air supply valve 84 to the tilting or dumping cylinder 70, which is then actuated to tilt the deck assembly and dump the material entrapped within its grooves 40, wehreupon the air supply is shut off and vented from the cylinder 70, allowing the spring 74 to return the deck assembly to its initial position. At this time, the timer appropriately actuates the high pressure air supply valve 62 leading to the feed bin cylinder 57, venting the latter and allowing the flow control valve 55 to reopen to permit the ore or other material in the feed bin 46 to again drop onto the upper end 44 of the porous deck. The entire interruption of ore feed caused by the dumping procedure, from the time the flow control valve 55 is first closed to the time of its reopening, may typically range from about 8 to 12 seconds, depending upon the extent of inclination or slope of the porous deck 34. The ore concentrating period may, for example, be about 4 minutes, the entire cycle time being variable depending upon the richness of the ore, that is, the percentage of the feed material to be recovered. The richer the ore, the shorter will be the cycle time so as to avoid losing valuable minerals to the tailings. Because of the relatively short period required for effecting the entire dumping operation, the apparatus is actually operating in the performance of its concentrating operation about 96 percent of the time.

The apparatus is comparatively simple, since it is movable only during the dumping operation. The air flowing through the static porous deck 34, coupled with the inclination of the deck,causes the material to flow from the upper end 44 of the deck to its lower end 45. Accordingly, it is evident that the motivating factors in producing flow of ore down along the bed are the vertical air stream flowing upwardly through the porous bed 34 and gravity. The entire deck assembly is moved only during the dumping cycle. Thus, complex auxiliary equipment is avoided, as in prior devices, and yet a high degree of recovery is effected. Moreover, the capacity of the apparatus is much greater than in prior devices, since the relative immobility of the deck 34 enables it to be made much longer and, therefore, capable of operating over a longer period during each cycle in effecting the settling of the heavyparticles into the grooves 40.

By way of example, a 1 foot by 6 foot porous deck has been found to be capable of handling from about 15 to more than 50 tons of ore in a 24-hour day, depending on grain size and the difference of density between the gangue and the heavy mineral values. This capacity increases the greater the density difference and the larger the grain size. Thus, coarse gold can be run at somewhat more than 50 tons per day per deck, while the light ores, such as malachite in fine grain size, would reduce the effective recovery capacity to 15 tons per day.

A typical cycle of operation is as follows:

a. An electrical timer impulse results in opening of the ore feed valve 55.

b. After a predetermined time for the low pressure air to fluidize the ore and effect a deposit of the heavier values in the grooves 40, the timer and the air cylinder 57 operate the feed valve 55 to a closed position.

' c. After about seconds (which is adjustable for each ore) for the ore blanket to flow off the lower end 45 of the deck 34 sufficiently, the timer opens the air valve 84 to the tilting cylinder 70 to effect dumping of the concentrate and the middlings into a suitable trough or other receiver.

(1. After about 2 seconds, the timer actuates the valve 84 to vent the tilting cylinder 70, allowing the spring 74 to return the deck 34 to its laterally horizontal position.

e. Immediately upon the return of the deck to the horizontal position, the timer operates the air valve 62 to vent the cylinder 57 and allow the ore feed valve 55 to open.

We claim:

1. In apparatus for separating intermixed materials of different specific gravities: a supporting structure; a plenum; a perforate pipe passing through said plenum; means mounting said pipe on said supporting structure; a porous deck mounted in said plenum and having spaced parallel grooves in its upper surface extending from the rearward portion of said deck to the forward portion of said deck; means for depositing the materials on the rearward portion of said deck; and means for conducting a gaseous medium into said pipe for discharge into said plenum and upward passage through said deck to effect fluidizing of the materials and their progression across said grooves from the rearward portion of said deck to the forward portion of said deck; said mounting means pivotally carrying said pipe on said supporting structure to enable said pipe, plenum and deck to be tilted between a normal position in which said grooves face upwardly and a tilted position in which the material of said grooves can be dumped from said deck.

2. In apparatus as defined in claim 1; said deck, pipe I and plenum being held in a stationary position while the materials are being fluidized.

3. In apparatus for separating intermixed materials of different specific gravities: a supporting structure; a plenum; a perforate pipe passing through said plenum; means mounting said pipe on said suporring structure; a porous deck mounted in said plenum and having spaced parallel grooves in its upper surface extending from the rearward portion of said deck to the forward portion of said deck; means for depositing the materials on the rearward portion of said deck; and means for conducting a gaseous medium into said pipe for discharge into said plenum and upward passage through said deck to effect fluidizing of the materials and their progression across said grooves from the rearward portion of said deck to the forward portion of said deck; said mounting means normally supporting said pipe, plenum and deck in a stationary position inclined to the horizontal downwardly from the rear portion of said deck to the forward portion of said deck; said mounting means pivotally carrying said pipe on said supporting structure to enable said pipe, plenum and deck to be tilted between its normal stationary position in which said grooves face upwardly and a tilted position in which the material in said grooves can be dumped from said deck.

4. In apparatus as defined in claim 3; said parallel grooves having downstream sides disposed at an acute angle to the upper face of said deck.

UNITED STATES a CERTIFICATE ()F Patent No. 3,777,887 LQQQQB QDeCeIHber 11, 1973 Ihventor(s) NORRIS JOHNSTON, "ET; AIJIT It is certified that error appears in 't-he'above-identified patent and that said Letters Patent are hereby eorrected as shown below:

Column 3', line 1, "pluralityf read the Signed and sealed this 16th Of July 1974 (SEAL) Attest:

MCCOY M. GIBSON', JR. 7 .c. MARSHALLDANN Attesting Officer I Comgni ssioner of Patents F ORM PO-105O (10-69) USCOMM-DC 60376-7 69 a as GOVERNMENI PRINTING OFFICE: 9'9 o-ase-au, 

1. In apparatus for separating intermixed materials of different specific gravities: a supporting structure; a plenum; a perforate pipe passing through said plenum; means mounting said pipe on said supporting structure; a porous deck mounted in said plenum and having spaced parallel grooves in its upper surface extending from the rearward portion of said deck to the forward portion of said deck; means for depositing the materials on the rearward portion of said deck; and means for conducting a gaseous medium into said pipe for discharge into said plenum and upward passage through said deck to effect fluidizing of the materials and their progression across said grooves from the rearward portion of said deck to the forward portion of said deck; said mounting means pivotally carrying said pipe on said supporting structure to enable said pipe, plenum and deck to be tilted between a normal position in which said grooves face upwardly and a tilted position in which the material of said grooves can be dumped from said deck.
 2. In apparatus as defined in claim 1; said deck, pipe and plenum being held in a stationary position while the materials are being fluidized.
 3. In apparatus for separating intermixed materials of different specific gravities: a supporting structure; a plenum; a perforate pipe passing through said plenum; means mounting said pipe on said suporring structure; a porous deck mounted in said plenum and having spaced parallel grooves in its upper surface extending from the rearward portion of said deck to the forward portion of said deck; means for depositing the materials on the rearward portion of said deck; and means for conducting a gaseous medium into said pipe for discharge into said plenum and upward passage through said deck to effect fluidizing of the materials and their progression across said grooves from the rearward portion of said deck to the forward portion of said deck; said mounting means normally supporting said pipe, plenum and deck in a stationary position inclined to the horizontal downwardly from the rear portion of said deck to the forward portion of said deck; said mounting means pivotally carrying said pipe on said supporting structure to enable said pipe, plenum and deck to be tilted between its normal stationary position in which said grooves face upwardly and a tilted position in which the material in said grooves can be dumped from said deck.
 4. In apparatus as defined in claim 3; said parallel grooves having downstream sides disposed at an acute angle to the upper face of said deck. 